To this day the joining method of riveting is predominantly used in the field of aircraft construction. Riveting is very well characterized with respect to its mechanical properties of the connection and the long-run behaviour during the life cycle of an aircraft. However, it does not fulfil the needs for weight optimization which are common in the field of light weight construction to a very high extent.
Therefore various other connection technologies have been developed and optimized to an extent so that they comply with the high security requirements which are common in the field of aviation while consistently implementing the principles of light weight construction. Hereunto belong for instance fusion welding methods like laser beam welding or electron beam welding, soldering or gluing.
However, riveting has the following drawbacks. For the inserting of the rivets boreholes are needed which implies a weaking. Moreover, drilling increases the requirements for corrosion protection. Furthermore the usage of rivets leads to an additional weight in the joint areas. Besides the apparative expenditure is high as well as the time need for the production of the joint. Beyond that extensive corrosion protection is required.
The fusion welding methods like laser beam welding, electron beam welding, et cetera have drawbacks as well. Fusion welding methods evoke a significant shape distortion due to the comparatively high heat introduction which frequently has to be corrected during the following production steps. Furthermore fusion welding methods are suitable only for metallic connections which are fusion weldable. This means they are suitable only for a small selection of the aluminium alloys which are used in aircraft construction. Further joining of two titanium components is possible only with extremely high apparative expenditure which is merely in singular cases economically profitable. Furthermore fusion welding methods require inert gases. Due to the generally high apparative expenditure which is needed for laser beam welding these methods are not suitable as a repair concept during the operation of the airplane.
Soldering also has similar drawbacks. During soldering both components to be joined have to be heated in an oven along with a solder located in the joint area up to the melting temperature of the solder. This results in a high thermal load in the components. Furthermore the apparative expenditure is high because the utilization of ovens is required. The airplane components frequently measuring several meters require accordingly sized ovens. In order to realize solder joints with very good mechanical properties high melting point solders are required, the method of hard soldering has to be applied. This leads to the fact that the components to be joined have to be brought up to the high melting temperature of the solder which generally exceeds 450° C. This makes the method unsuitable for aluminium alloys because they loose their good mechanical properties at such high temperatures. Due to the generally high apparative expenditure which is needed for soldering it is not suitable as a repair concept during the operation of the airplane as well.
Regarding to the drawbacks of gluing, glued connections are not electrically conductive. This constitutes a challenge especially to the protection against lightning stroke on airplanes. The glued connections commonly used in aviation require the exposure to raised temperatures for certain periods of time which results in a temperature stress of the components to be connected. Furthermore, the long-term durability and the temperature durability of glued connections are still subject to inquiries.
Friction stir welding has several disadvantages as well. This method is suitable only for metallic connections, especially for low melting light metal alloys from aluminium or magnesium. For joints of titanium components the apparitive expenditure rises tremendously. Friction stir welding is therefore not suitable as a repair concept during the operation of the airplane.
In the state of the art, as disclosed in DE 103 34 391, a method is known for generating connections in the field of microelectronics. In this method a reactive material and a solder is arranged between two components, wherein an exothermic reaction is caused in the reactive material by an ignition. In this exothermic reaction the solder melts and results in a connection of both parts.
However, in such a method only very small microelectronic components are connected to each other. Such a method is neither intended nor suitable for connecting big structure elements in aircraft construction like skin plates and skins respectively, stringers, formers, clips and/or comb-like formers to each other. Furthermore skins of airplanes for instance can reach dimensions of up to several meters. Also the requirements with respect to the mechanical properties of the joint in the field of microelectronics are clearly different from the requirements in the field of aircraft construction.